1. Field of the Invention
The invention deals with a surgical drilling device and subsequent drilling procedure aiming at drilling holes in live human or animal bones. The device is equipped with a drilling drive rotating a drilling tool that conducts electrical currency.
2. Description of the Prior Art
Orthopedic surgery and trauma care require bone drilling when repair of fractures is indicated. The holes resulting from drilling accept screws to hold implants such as plates, prostheses or to exert pressure between broken and subsequently reduced bone fragments. The screws inserted have to fit allowing a length range of no more than one millimeter. Conventional measuring of length is using a mechanical slide gauge, which is unhandy, time consuming and erratic, sometimes requiring repeated x-ray-control and corrections, yet even tissue injury in rare cases.
The bones in question usually are of two major structures: cortical bone, which for example is stress carrying entity in tube-shaped long bones, and spongious bone, which e.g. is accumulated in the vicinity of joint surfaces.
Passing with a drill through a tube-shaped bone perpendicular to the long axis means penetrating at first the cortical layer, followed by spongious bone and reaching out through the opposite cortical layer to touch soft tissue surrounding the bone. The opposite cortex is normally covered by soft tissue, whereas the at the starting point, the small area, where the drill is attached before drilling on the nearside cortex is being either surgically exposed or reached transcutaneously by palpation with the aid of a socket. This socket protects soft tissue from immediate contact with the drill and equally helps to guide the drill, to give it the direction of choice.
Alternative matters to determine the depth of the drilled hole are provided by ultrasound techniques or use of lasers. These methods refer to variable reflections from soft tissue, cortical and spongious bone. These methods, however, are technically demanding and need separate measuring—as with the slide gauge—by interrupting the drilling act.
When drilling through bones, at the end the surgeon has to take care of the adjacent soft tissue after penetration the opposite cortex, thus to prevent this tissue from being injured. To make sure that this does not happen, some surgeons interrupt the drilling act in order to palpate with the non-rotating drill whether or not the cortex is penetrated. It is the object of this invention to simplify this manoeuvre by sparing the surgeon this interruption and simultaneously indicating the depth of the bore hole. This technical ability is provided by the demand number one of this invention. Furthermore, the invention in question refers to a medical drilling device which is equipped with a bore electrode (incorporated in the drill), a backing electrode as well as a measuring device for electrical resistance connecting both electrodes. Thus, the bore electrode is directly connected with the current conducting drilling device, while the backing electrode is mounted at an opposite distance to the drilling device, e.g. on the skin of the patient.
With the aid of the resistance measuring device, the two electrodes are exposed to continuous or alternating electrical current. Subsequently, the electrical resistance between the bore electrode and the backing electrode can be measured and indicated on a monitoring screen.